In general, an imaging device including an endoscope or a laparoscope includes a light source, a lens and a sensor (camera) for acquiring the light reflected from the object. In an endoscope, laparoscope or other imaging systems, imaging device takes the reflected light from the object where the light source is usually a white light. The use of a fluorescent imaging system is increasing as it helps diagnose specific diseases by imaging the fluorescent emission from the object illuminated by an excitation light having a particular wavelength.
The fluorescent material can be present within a living body or may be injected from outside the body. Fluorescence due to the intrinsic fluorescent material is called autofluorescence. Autofluorescence changes by the biological condition or disease. Measuring the change of it can help diagnose the disease. Injected fluorescent material can also be helpful as the distribution of fluorescence changes by the biological condition.
In the imaging device such as an endoscope, laparoscope or fluorescence, a normal light image which is a reflection of white light is the primary image, and fluorescent image serves only as a supplementary. Thus, the natural reflected image is more frequently used, and seldom required only the fluorescent image. It is advantageous to include a normal light image even in the fluorescent imagery. For example, when the resection of the tumor is performed using a fluorescence imaging system, it is safer to see both the normal light image and the fluorescent image as that may reveal particular conditions of the surrounding normal tissues and vessels.
A conventional imaging method to obtain a normal light image, a reflected image, and a fluorescent image uses mirrors to change the sources and light path mechanically, or beam splitters to separately obtain each image, along with multiple light sources and multi-mode cameras. The method using mirrors is described in the U.S. Pat. No. 7,722,534.
Such methods have disadvantages like low durability and may show early mechanical failure due to the complex structure, and only a limited amount of light received as the images are acquired in a time-sharing manner. Using a beam splitter also suffers from a reduced amount of input light as it divides and distributes light for multiple targets. The previous method for obtaining a normal light image and fluorescent image together cannot help but to rely on such complicated methods as the wavelength of the emitted fluorescent light lies inside the spectrum of the white light which is continuous over the spectrum range. As far as the illumination source is a white light having continuous spectrum, simultaneous acquisition of the normal light image and the fluorescent image is impossible.
The reason is that the wavelength of the white light source ranges between 350˜750 nm and sometimes expands further over 750 nm including infra-red-light range. The emitted fluorescent light mixes with the reflected white light, and it cannot be separated.